1. Field of the Invention
The present invention relates to a paper feed roller employed for paper feeding in an electrostatic copier or a printer.
2. Description of Related Art
A paper feed roller is built in a paper feed mechanism provided in an apparatus such as an electrostatic copier, a laser beam printer, a plain paper facsimile, an ink jet printer or an automatic teller machine (ATM), for example. The paper feed roller includes a feed roller, a transport roller, a platen roller or a paper discharge roller rotating in contact with papers (including plastic films or the like: this also applies to the following description) for transporting the papers by friction.
In general, a rubber roller made of natural rubber, urethane rubber, ethylene-propylene-diene rubber (EPDM), polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber or the like, for example, is employed as the paper feed roller.
The outer peripheral surface of the paper feed roller coming into contact with the papers may be roughened, knurled or embossed, in order to achieve excellent paper feeding by increasing the friction coefficient with respect to the papers. However, the outer peripheral surface subjected to such processing is so easily abraded that the friction coefficient may be reduced due to abrasion upon repetitive contact with the papers, to result in defective transportation of the papers in a relatively early stage.
In recent years, papers containing a large quantity of low-priced extender such as calcium carbonate or talc and a low-priced sizing agent (bleeding inhibitor) prepared from aliphatic hydrocarbon for reducing the cost have been on the market as papers for the aforementioned apparatus. In such papers, however, a large quantity of paper dust results mainly from the calcium carbonate or talc, and easily adheres to the outer peripheral surface of the paper feed roller. Thus, the friction coefficient of the paper feed roller may be reduced due to the adhesion of the paper dust, to cause defective transportation of the papers in a relatively early stage.
Various studies have been made in order to prevent such adhesion of the paper dust. For example, Patent Document 1 (Japanese Unexamined Patent Publication No. 5-125142 (1993)) describes that adhesion of paper dust resulting from static electricity can be suppressed by reducing electric resistance of a paper feed roller. Patent Document 2 (Japanese Unexamined Patent Publication No. 2003-2481) describes that adhesion of paper dust can be suppressed by adding a flaky filler into rubber forming a paper feed roller. Patent Document 3 (Japanese Unexamined Patent Publication No. 2004-299842) describes that adhesion of paper dust can be suppressed by embossing the outer peripheral surface of a paper feed roller and finely irregularizing the embossed outer peripheral surface.